In general, semiconductor devices such as vertical cavity surface emitting lasers (VCSEL) are constructed by providing a substrate with very smooth surface. A first stack of mirrors is then grown on the surface by semiconductor manufacturing techniques. An active area is grown on the upper surface of the first mirror stack and a second mirror stack is grown on the upper surface of the active area. Generally, metal contacts formed of an easily deposited metal, such as gold, titanium, tungsten, platinum, or the like, are provided. In general, one metal contact is provided in contact with the surface of the first (lower) mirror stack and a second metal contact on the upper surface of the second mirror stack.
One problem that occurs in VCSELs is to contain the lasing, or optical mode to a lowest order mode and to contain current flow to approximately the volume of the VCSEL in which lasing is occurring. Higher order lasing and extraneous flow of current outside the lasing area produces heat in the VCSEL and causes a substantial loss of power. Ridge, or top emitting mesa shaped, VCSELs are the preferred implementation over planar VCSELs because of the better current confinement and optical guiding.
In the fabrication of top emitting VCSELs, the alignment of the top electrical contact to the light emitting area is very important. Any misalignment of the electrical contact on the upper surface reduces the efficiency of the VCSEL. Further, the contact metal generally covers the sidewall of the mesa as a reflector to reduce the optical loss and increase efficiency. The problem is that the metal contacts are not sufficiently large in area and are generally too thin to effectively conduct heat generated within the VCSEL away from the VCSEL. In many instances large and heavy metal heat sinks are affixed to the VCSEL to absorb the heat. These are unsatisfactory for a number of reasons: they are large and bulky, they do not efficiently spread the heat, and the VCSEL is seldom constructed so that the heat sink can be positioned in close proximity to the source of the heat. For example, the heat sink is generally positioned on the rear surface of the substrate so that only heat traveling through the substrate, which is generally formed of poor heat conducting material such as gallium arsenide (GaAs), reaches the heat sink. A major portion of the heat remains in the VCSEL.
Accordingly, it is a purpose of the present invention to provide a new and improved VCSEL with heat conductivity.
It is a further purpose of the present invention to provide a new and improved VCSEL with heat conductivity which does not require a large and heavy heat sink.
It is a still further purpose of the present invention to provide a new and improved VCSEL with heat conductivity which is formed as additional steps of the fabrication process.
It is another purpose of the present invention to provide a new and improved VCSEL with heat conductivity in which heat conduction and spreading material is positioned adjacent heat generating portions of the VCSEL.